Variable resistance device



Oct. yZ4, 1939. N. c. scHr-:LLENGr-:R 2,177,285

' VARIABLE RESISTANCE DEVICE I Filed March s, 1957 2 sneetssheet 1 H /6Il "2 Z5 /s `zo ATT'VS.

Oct. 24, 1939..- N. c. scHELLENGr-:R 2,177,285

VARIABLE RESISTANCE DEVICE Filed March s, 1957 2 sheets-sheet 2 .n l ss\\\\\\\\\\\\\\\\\\\\\i| i ATTYS.

VPatented Oct. 24, 1939 i UNITED STATES i autres VARIABLE RESISTANCEDEVICE Newtonl C. Schellenger, Elkhart, Ind., assigner to ChicagoTelephone Supply Company, Elkhart, Ind., a corporation of IndianaApplication March 8, 1937, Serial No. 129,553

14 Claims.

This yinvention relates to a new and improved variable resistance andmore particularly to a compact type of device especially adapted. fori'e in connection with radio apparatus or the The present trend withmany types of `radio receivers and of radio test apparatus is towardreduction in size of the assembly and consequently there lis a demandfor variable resistances l i which will occupy a minimum of space uponthe chassis or in the set housing. This trend is especially present inautomobile radio receivers. It is customary with automobile receivers tolocate a control head at a distance from the set g proper and to connectthe head to the set by means of flexible shafts. The usual construetioninvolves two such shafts, one of which controls the tuning condenser andthe other of which controls the volume control of the set, which controlis in the form of a variable resistance. The control heads are small insize and it has not been considered practical to install the variableresistance in the head. It is customary to provide a pilot light in thehead connected to the radio set by a shielded cable and with a compactvariable resistance mounted on the head thisA cable can carry thenecessary conductors with a saving in the expense of one oi' the exibleshafts, and of the space taken in the set by the variable 3@ resistance.

Many types of automobile receivers are also provided with a tone controlin the form of a variable resistance. These devices in some cases aremounted in the set to be operated by a knob 35 on the set itself and inother ca'ses are mounted on the control head.

According to the present invention I provide a variable resistanceentirely contained within a knob of the size usually used for operatingsuch ed variable resistances. The only projections from the knob'are asecuring screw or 'shaft and the necessary terminals for electricalconnection to the variable resistance.

It is an object of the present invention topro- Vide a new and improvedvariable resistance.

It is a further object to provide a device of this character which iscompact in size and adapted to have its working parts enclosed within anoperating member or knob.

It is also an object to provide a device comprisingv a resistanceelement having a convex conits .tact'surface and a contacter normallyfiat and` flexed by engagement with the convex surface.

55 1t is another object to provide a device having ilxed terminalsyieldingly urged into contact with the resistance element.

It is an additional object to provide a device in which the severalterminals are secured in position in the device by means of deformatt'onof 5 the terminals and without the use of rivets or other separatesecuring devices.

1t is a further object to provide a contact construction in which thecontacter and collector ring are integral. l0

It is also an object to provide a contactar construction in which thecontacter engages a convex surface by means of a concave surface ofgreater radius of curvature and in which the contactor is positivelydriven in either direction from l5 points below the line of tangencydrawn through the line of engagement between the contact and resistance.

It is anotherrobject to provide a contact of the character describedhaving a plurality of spaced, 20 separately iiexed contact elements.

It is an additional object to provide a variable resistance constructionin which a resistance strip is located and positioned by integrallyformed means on the base and resistance strip. 25

It is a further object to provide a construction in which the base isprovided with openings into which end, intermediate, and movable contactterminals may be selectively tted as desired.

It is also an object to provide a variable resistance device in whichthe operating knob houses the parts and directly drives the movablecontact.

Itis another object to provide such a construction in which the housingknob has a central bearingon a shaft and a second bearing of its skirtagainst the periphery of the base, with coacting stops formed in thehousing and base.

It is an additional object to provide a device which is compact andcomprises few parts designed for commercial production and assembly.

Other and further objects will appear as the description proceeds.

I have shown a preferred embodiment of my invention in the accompanyingdrawings in which- Figure 1 is an elevation of one form of constructionof the device;

Figure 2 is a view of Figure 1 as seen from the 50 right;

Figure 3 is a section taken on line 3-3 of Figure 2; s

Figure 4 is a fragmentary section taken on line 4-4 of Figure 2; 5f

Figure 5 is a section taken on line l-l oi Figure 3;

Figure 6 is an elevation, partly broken away, oi' the b ase with theresistance element assembled thereon; j

Figure 'l is a perspective. partly broken away, of the resistanceelement;

Figure 8 is a perspective view oi an end terminal member;

Figure 9 is a perspective view of the terminal spring;

Figure 10 is a perspective view of. the terminal making sliding contactwith the movable contact member;

Figure 11 is a perspective view of the new movable contact member;

Figure 12 is a fragmentary section, similar to Figure 4, showing amodiiied form of endor intermediate terminal; and

Figure 13 is a perspective view oi the terminal of Figure 12.

In the drawings, the base member I5 which is formed ot insulation, isprovided with a bottom ange I6 which has formed therein a groove-I1which serves to receive the resistance element I 8. The base member I5may be formed oi.' any -suitable insulation material, such, for example,

as Bakelite, and may be made by a molding process. The resistanceelement, as shown in Figure 7, is preferably a exible strip of fibre orother similar insulating material, which carries a rel sistance illmsprayed or otherwise suitably ap plied to the .outer cylindrical surfacethereof. The resistance element IB is provided on its lower edge with alug or extension i! which, as shown in Figure 6, 4fits into acorresponding recess 2U in the base oi the groove I'I in the base menz-`ber I5.

The base member i5 is further provided with a plurality of openings 22extending therethrough, these openings being shown in Figures 3 andi.These openings 22 have reduced portions 23 extending through the. loweror bottom portion of the base member. As shown in Figure 2, the basemember is provided with five such openings in two spaced groups ot twoand three respectively. These groups are` located in arcuate extendedportions 24 and 25 on the bottom of the base member. These extendedportions may be fitted in corresponding openings in a mounting 'l plateor set chassis to locate the base member thereon and to serve asinsulation between the chassis or plate and the terminals which extendthrough two or more of the openings.

The axis oi.' the base member I 5 is provided with a cylindrical openingwhich receives the mounting stud or bolt 23. This bolt 26 has a threadedinner end 21 which will pass through the mounting'plate or chassis andreceive a nut to secure the device ,in place. 'I'he boit l2i also has anenlarged head 23 which' dts in the cupshaped rotatable housing member 23to retain it in position upon the base member Il. The bolt 26 is furtherprovided with a shoulderjll en- Easing the upper or outer face of themember AIl so as to properly position the housing 2l Afor roationwithout binding.'

The housing 2! is provided with a knurled edge 2|, as best shown inFigure 1, so as to facilitate its `manipulation and rotation. As alsoshown in Figure 1, the depending skirt 32 of the housing 2l isprovided.with a lug' adapted to engage the lug N Iorme'd on the basemember Il for the purpose or limiting rotation of the housing ineitberdirection. Y

'Ihe end terminals 35 are ntted in the openmgs 22 and have reverselybent portions 36 which engage the upper edge of the resistance strip Iladjacent its ends.` One of these terminals is shown in perspective inFigure 8, and its location and engagement is shown in Figure 4. Thespring 31 which is fitted in the opening 22 with the terminal urges theterminal toward the axis of the base member I3 and thus serves to pressthe reversely bent portion 3S of the terminal iirmly against the upper.edge of the resistance element I 3. Consequently there will be adequatepressure and' the proper electrical contact between the terminal and theresistance strip throughout the liie of the device, since thisconnection will not be modiiled by changes in ternperature or humidity.AIt is to be noted that the portion 36 engages only the upper edge ofthe resistance strip so that the main portion ot the strip is availablefor contact by the rotatable contact member throughout the full arccovered by the strip.

The terminals 35 are each provided with an oii'set portion 50 which, asshown in Figures 3 and 4, seats against the bottom of the larger portionof the opening 22 adjacent the reduced porf tion 23 of the opening. Thisseating positively limits the downward movement of the contact, which ispreferably made oi' such length that there is a slight clearance betweenthe terminal member and' the upper edge of the base wall against whichthe resistance strip seats. This prevents any flexing of the radiallyextending portion ofthe terminal such as might adversely aii'ect uniformcontact with the resistance strip. It will be understood that similarterminals may be inserted in the additional openings 22, shown in Figure5, to provide intermediate taps if desired. Since the terminals engagethe resistance strips only adjacent the edge, the same type o! terminalmay be used at the ends or at `any intermediate point.

After the terminals have been put in place, the connection end 33 ofeach terminal is `twisted through a substantial arc so as to iirmlyretain the terminal in place with the offset portion 5I against the basemember and to prevent the terminal being drawn or forced back into thebody oi the device.

Thtermi'nal which makes sliding connection with the movable contact isshown in detail in Figure 10, and also is shown in Figures 3 and 5. Thismember has a body portion Il which fits in one oi' the openings 22 andhas a connection por-l tion It passing through the reduced opening 23 ladapted to seat against the oppositelside of the opening 22 from thebody portion and thus firmly locate the terminal in the base member- II.

Extending from the upper end o1' the reversely bent portion 4I lare thearcuate arms J2 and l2.

Thev arms I2 and l2 are provided with the up- 'the member I4 andconsequently enum dinerent circular paths'onY that element. This servesto vminimise wear and each contact forms a path to gvsuitits own contourso-thata highly emcient sliding contact is had throughout along life andcontinued use of the device. The rotatable contact element 44 is fittedin suitable recesses formed in the base and skirts of the rotatable`housing 29.

The member 44 has a depending locating portion 45 at one side and at theopposite side is provided with a circumferentially extending arm 46terminating in the downwardly extending portion 41. From the portion 41extend the spaced contact portions 48, the opposite ends of which arejoined by the portion 49. These contact portions 48 engage the surfaceof the resistance strip I8, as clearly shown in Figures 3, 4 and 5 ofthe drawings. It will be noted thatl these members 48 are normally atand are caused to have a slightly concave form in operation, due to theradial pressure exerted upon them by the resistance strip I8. It istherefore possible to manufacture the devices with very uniform contactpressure since the pressure is not dependent upon any permanentdeformation of the spring material forming the contact. It will also beapparent from Figure that the thrust which moves the contact members 48is exerted in a plane below the plane of tangency at the point ofcontact between the members 48 and the resistance strip I8. 'Ihis isimportant as the thrust exerted in this direction does not cause anytendency for the contacts to bite into the resistance strip. It will beapparent that the contacts 48 are moved in one direction by a thrustfrom the rotatable housing 29 against .the member 41 and are moved inthe opposite direction by a thrust from the housing 29 against themember 49. Consequently, in either direction the contacts are positivelypushed.

The member 43 is unitary so that there is only a single sliding contactconnection vbetween the point of engagement with the resistance elementand the solder lug end of the member 40. The contact bars 48 are spacedapart a considerable distance and are' connected only at their ends.Thus they are substantially independent of each other in their contactaction which assures an efficient contact with the resistance elementeven types of contactors, the metal is broken. This may not be apparentto the eye but is shown by the microscope. Such a broken surfacegradually abradesand wears the`resistance element causing a change inthe resistance value during the life of the unit. 'I'he smooth, unbrokensurfaces of the contacts `of the present invention glide over theresistance surface without appreciable abrasion of the surface in manythousands of operations of the device.

A modified form of terminal contact member 58 is shown in Figure 13 andis shown in assembled position. This member 53 is similar to the member35 except for the fact that it is formed of resilient metal and has anintermediate outwardly bent portion to serve Vthe same function as theseparate spring member 31 of the form of construction shown in Figure 4.It is provided with the downturned resistance engaging portion 55, theseating onset portion 58 and the solder lug end portion 81. The terminalof Figures 12 and 13 must be made of spring stock while the terminal ofFigures 4 and 8 need not be made of spring stock since the resilientgripping action is provided by the separate spring 31.

The raised portions 24 and 25 on the bottom of the base member I5 servethe function of providing better insulation between the terminals andalso serve, when seated in similar openings in a chassis or othersupport, to prevent rotation of the base and insulate the terminals fromthe support.

My improvedvariable resistance is composed of but few parts and theassembly is extremely simple since no separate eyelets or rivets areused. This also insures permanently efficient connections, as eyeletsand rivets tend .to gradually work loose, especially when used uponvbases formed of synthetic resins which shrink slots in said base, aresistance element located against the outer face of the base, terminalsextending through the slots in the base and having reversely bentportions engaging the outer face of the resistance element,andAresilient means within the slots urging said terminal portionsagainst the resistance element.

2. In a variable resistance device, a base, a cylindrical resistanceelement carried by rthe base, a cup-shaped housing enclosing theresistance element and rotatably mounted on the base, a movable contactcarried by the inner face of the skirt of the housing and having anintermediate portion in engagement with the outer face of the resistanceelement, said contact having its ends positively driven by the housing.

3. In a variable resistance device, a base, a cylindrical resistanceelement carried by the base, a cup-shaped housing enclosing theresistance element and rotatably mounted on the base, a movable contactcarried by the inner face of the skirt of the housing in engagement withthe outer face of the resistance element, said contact having its endspositively driven by the housling, and having an intermediate portionspaced from the housing and flexed by engagement with the resistanceelement to provide a concave surface in contact with the convex surfaceof the resistance element.

4. In a variable resistance device, Va base, a resistance elementcarried by the base, said re'- sistance element having an outercylindrical contact surface, a cup-shaped rotatable housing enclosingsaid resistance, a movable contact car.- ried by the inner surface ofthe cup-'shaped housing, said contact comprising a ring carried in thebase of the cup and an integral contact portion extending against thelateral Wall of the cup tangentially of the resistance element, the wallhaving a recess formed therein to receive the contact portion -and topositively drive the contact portion upon rotation of the housing ineither direction, and a connecting member carried by the base andengaging the ring.

5. In alvariable resistance device, a base, a

resistance element carried by the base, saidY resistance element havingan outer cylindrical contact surface, a cup-shaped rotatable housingenclosing said resistance, a movable contact carried by the innersurface of the cup-shaped housing, said contact comprising a ringcarried in the base ot the cup, a locating arm extending from one sideof the ring and an integralcontact portion extending from the oppositeside of the ring, the lateral wall of the cup havingrecesses therein toreceive the locating arm and contact portion, and a connecting membercarried by the base and engaging the ring.

.6. In a variable resistance device, a base member having a lateralwall, a resistance element adjacent the lateral wall, the base memberhaving an opening extending through said member adjacent the lateralwall, a terminal in said opening, one end ci the terminal extendingbeyond the upper wall of the base and reversely bent to engage the outerface of the resistance element, and resilient means in the openingurging the terminal in such direction as to force the reversely bentportion reiiiently against the resistance element.

7. A variable resistance device comprising a base, a cylindricalresistance member carried by the base, a rotatable member having aportion movable about the outer face of the resistance member, and amovable contact extending tangentially of the resistance member andcarried by said portion of the rotatable member in engagement with theouter face of the resistance element, said contact comprising a datstrip of metal of substantial size having both ends positively engagedby the rotatable member whereby the contact is positively pushed in eachdirection of rotation.

8. A variable resistance device comprising a base, a cylindricalresistance member carried by the base, a rotatable member havingv aportion movable about the outer face of the resistance member, andamovable contact carried'by said portion of the rotatable member inengagement with the outer face of the resistance element, said contactbeing positively driven by the rotatable member in both directions, saidcontact having a normally fiatA intermediate resistance engagingportion, said intermediate portion being outwardly flexed by engagementwith the resistance element to provide a concave surface in contact withthe convex surface of the resistance element.

9.l A variable resistance device comprising a base, a cylindricalresistance member carried by the base, a rotatable member having aportion movable about the outer face oi' the resistance member, and amovable contact carried by said portion oi the rotatable member inengagement with the outer face of the resistance element, said contactbeing positively driven by the rotatable member in both directions, saidcontact having a normally flat intermediate resistance engaging portion,said intermediate portion being outwardly flexed by engagement with theresistance element to provide a concave surface in contact with theconvex surface of the resistance element, the positive drive of thecontact element being from points closer to the axis of rotation of therotatable member than a line drawn tangent to the resistance element atthe point of contact.

l0. A variable resistance device comprising a base, a cylindricalresistance memberl mounted on the base, a rotatable member adjacent theouter iace of the cylindrical resistance member, and a movable contactmember carried against the outer face of the resistance element by saidrotatable member, said contact member comprising a plurality of spaced,normally dat portions iiexed by engagement with the resistance element,said plurality of portions being integrally Joined at their ends andbeing pushed in either direction by the rotatable member.

11. In a. volume control device: a base; a control member mounted overthe base, variable resistance means carried by the base and controlmember and actuated by movement of one with respect to the other; meansengageable with the base and a support with which the base is associatedfor securing the base to the support; terminals projecting from the baseadjacent to said securing means and connectible with instrumentalitiesat the opposite side of said support; and raised portions on the baseadjacent to said support, said raised portions being unlike and havingareas substantially less than that of the base, and extending betweenand around the terminals; said raised portions being adapted to coactwith openings in the support to hold the terminals spaced from the edgesof the openings, and coasting with said securing means to locate thedevice relative to the support and prevent its rotation with respect tothe support.

l2. In a circuit control device, a base, the base having an openingtherethrough, said opening having a narrow iiat portion adjacent oneface of the base and an inner shoulder formed in the base adjacent saidnarrow portion, a terminal .member extending through the opening, a bentportion of the terminal engaging the inner shoulder, and the terminalmember being twisted adjacent the opposite face of the base to retainthe terminal in place.

13. In a variable resistance device, a base, s cylindrical resistanceelement carried by the base, a cup-shaped housing enclosing theresistance element and rotatably mounted on the base, said housinghaving spaced shoulders on its inner face. a movable contact comprisinga hat strip oi metal of substantial size carried by the inner face oithe skirt of the housing with its ends engaging the shoulders on thehousing, and an intermediate portion of the contact in engagement withthe outer cylindrical face of the resistance element, said contact beingnormally fiat and being iiexed by engagement with the convex surface o1'the resistance element.

14. A variable resistance device comprising: a base of insulatingmaterial having a cavity therein; a resistance element embracing aportion o! the external surface I the base; a contact in said cavitywith its inner end having a portion engaging the outer surface of saidresistance element and with its outer end projecting from the basethrough a restricted opening leading from the cavity to the adjacent endof the base; the junction between the inner end of said opening and thecavity defining a shoulder within the base: means on said contactengaging said shoulder to limit movement of thecontact with respect tothe base in one direction; a shoulder on the end o! the contactprojecting from the base and engageable with the base for limitingmotion between the contact and the base in the opposite direction, saidlast named shoulder being formed by twisting the end of the contactoutwardly of said restricted opening out of alignment with the generalplane of the Contact; and spring means between the contact and one wallo1' the cavity for yieldingly maintaining the inner end of the contactengaged With the resistance element.

NEWTON C. SCHEILENGER.

